In an internal combustion engine of a vehicle, there is an internal combustion engine having an air-fuel ratio control unit of the fuel jet type as a countermeasure to the problems of harmful exhaust components, fuel consumption ratio, and the like. The air-fuel ratio control unit adjusts an injection amount as an amount of fuel which is supplied to the internal combustion engine by signals from various kinds of sensors such as a throttle opening degree sensor to detect an operating state of the internal combustion engine, an engine rotational speed sensor, and the like, thereby controlling the air-fuel ratio.
In the above air-fuel ratio control unit, a front O.sub.2 sensor serving as a first exhaust sensor is provided on the exhaust passage upstream of a catalyst material, a rear O.sub.2 sensor serving as a second exhaust sensor is provided on the exhaust passage downstream of the catalyst material, the front and rear O.sub.2 sensors are connected to control means, and the control means performs a dual O.sub.2 feedback control in a manner such that the air-fuel ratio is first feedback controlled to a value in a stationary operating range of the internal combustion engine by a first detection signal from the front O.sub.2 sensor, the air-fuel ratio is open controlled in case of an acceleration/deceleration operating state other than the stationary operating range of the internal combustion engine, and when the second feedback control performing conditions are satisfied, the air-fuel ratio is second feedback controlled by a second detection signal from the rear O.sub.2 sensor, and the air-fuel ratio is open controlled in cases other than the second feedback control performing conditions.
In the internal combustion engine having the above air-fuel ratio control unit, there is also a catalyst deterioration judging apparatus for judging and diagnosing a deterioration of the catalyst material.
As a catalyst deterioration judging apparatus of the internal combustion engine, there is an apparatus disclosed in JP-A-4-109045. The air-fuel ratio control method and apparatus disclosed in this publication comprises: purifying means provided in an exhaust pipe of the internal combustion engine; air-fuel ratio detecting means arranged on each of the upstream side and the downstream side of the purifying means; fuel supplying means for supplying a fuel to cylinders of the internal combustion engine; and electronic control means for receiving detection signals from the air-fuel ratio detecting means and for controlling the fuel supplying means, wherein an air-fuel ratio of mixture gases which are supplied to the cylinders of the internal combustion engine is controlled on the basis of a detection signal of the air-fuel ratio detecting means on the upstream side, and the control means monitors a deterioration of the purifying means in accordance with a response change of the detection signal of the air-fuel ratio detecting means on the downstream side when a target value of the air-fuel ratio is changed, thereby enabling the presence or absence of the deterioration of the catalyst to be judged in a relatively short time and at a high reliability.
There is also an apparatus disclosed in JP-A-4-116239. According to a catalyst deterioration diagnosing apparatus of an internal combustion engine disclosed in the latter publication, when a deterioration of the catalyst is judged by comparing an output of an air-fuel ratio sensor on the upstream side of a catalytic converter and an output of an air-fuel ratio sensor on the downstream side, in the case where the updating of the learning correction using the downstream side sensor is not sufficiently executed, its diagnosis is inhibited, thereby preventing a decrease in diagnosing precision due to an actual deviation of the air-fuel ratio itself or a variation of a judgment reference.
A conventional catalyst deterioration judging apparatus of an internal combustion engine judges a deterioration state of a catalyst material in a catalytic converter. However, there is not known a catalyst deterioration judging apparatus which functions to judge deterioration states of two exhaust sensors which sandwich the catalyst material therebetween, and particularly the deterioration state of the front O.sub.2 sensor.
Although there is no inconvenience in the ordinary use state of a vehicle, for example, in case of using leaded gasoline, the engine is subjected to the poison property of lead in leaded gasoline. There are inconveniences in that the function of the catalyst material in the catalytic converter and the function of the front O.sub.2 sensor remarkably deteriorate, the exhaust gas purifying function of the catalyst material in the catalytic converter deteriorates, and the controllability of the air-fuel ratio of the front O.sub.2 sensor deteriorates.
Further, in the case where a high tension cord is pulled out and an accidental fire occurs due to an unexpected accident, the catalyst material in the catalytic converter or the front O.sub.2 sensor is damaged. In a manner similar to the case of using leaded gasoline as mentioned above, there are inconveniences in that the function of the catalyst material in the catalytic converter or the function of the front O.sub.2 sensor remarkably deteriorates, the exhaust gas purifying function of the catalyst material in the catalytic converter deteriorates, and the controllability of the air-fuel ratio of the front O.sub.2 sensor deteriorates.
To eliminate the above inconveniences, according to a first embodiment of the present invention, there is provided a catalyst deterioration judging apparatus of an internal combustion engine in which a first exhaust sensor is provided on an exhaust passage of the internal combustion engine on the upstream side of a catalyst material, a second exhaust sensor is provided on the exhaust passage on the catalyst downstream side, and a deterioration of the catalyst material is judged while feedback controlling an air fuel ratio by detection signals of the first and second exhaust sensors, characterized by control means having judging function which is constructed in a manner such that upon judgment of a deterioration, a feedback correction amount is set to be larger than that in the ordinary state, a dual exhaust sensor feedback control is stopped, a rich judgment delay time and a lean judgment delay time are set in accordance with a ratio at the time of an ordinary dual exhaust sensor feedback control so as to set a rich/lean judgment delay time to a predetermined time, the feedback correction amount is set to a deterioration judgment value, a second exhaust sensor response delay time is corrected by an engine load and an exhaust temperature, and the value is corrected by a period of a first exhaust sensor period of time, the second exhaust sensor response time after completion of the correction is compared with said deterioration. judgment value, and the deterioration of the catalyst material is judged.
There is also provided a catalyst deterioration judging apparatus of an internal combustion engine in which a first exhaust sensor is provided on an exhaust passage of the internal combustion engine on the upstream side of a catalyst material, a second exhaust sensor is provided on the exhaust passage on the catalyst downstream side, and a deterioration of the catalyst material is judged while feedback controlling an air fuel ratio by detection signals of the first and second exhaust sensors, characterized by control means having a function which is constructed in a manner such that a rich judgment delay time and a lean judgment delay time are set in accordance with a ratio at the time of an ordinary dual exhaust sensor feedback control, and when a rich/lean judgment delay time is set to a predetermined time, variation characteristics of an output performance of the first exhaust sensor are measured by the first exhaust sensor period of time, and the deterioration judgment value is corrected by the variation characteristics.
According to the invention as mentioned above, when the deterioration is judged by the control means, the feedback correction amount is set to be larger than that in the ordinary state, the dual exhaust sensor feedback control is stopped, the rich judgment delay time and the lean judgment delay time are set in accordance with the ratio at the time of the ordinary dual exhaust sensor feedback control so that the rich/lean judgment delay time is set to a predetermined time, the feedback correction amount is set to the deterioration judgment value, the second exhaust sensor response delay time is corrected by the engine load and the exhaust temperature, the above value is corrected by the period of the first exhaust sensor period time, the second exhaust sensor response delay time after completion of the correction is compared with the deterioration judgment value, and the deterioration of the catalyst material is judged. On the other hand, the rich judgment delay time and the lean judgment delay time are set in accordance with the ratio at the time of the ordinary dual exhaust sensor feedback control, and when the rich/lean judgment delay time is set to a predetermined value, the variation characteristics of the output performance of the first exhaust sensor are measured by the first exhaust sensor period time, and the deterioration judgment value is corrected in accordance with the variation characteristics by the control means.
The present invention also provides an apparatus for judging a deterioration of a catalyst of an internal combustion engine in which a first exhaust sensor is provided on an exhaust passage of the internal combustion engine on the upstream side of a catalyst material, a second exhaust sensor is provided on the exhaust passage on the downstream side of the catalyst material, a first feedback control is performed to set an air-fuel ratio to a target value on the basis of a first feedback control value which is calculated from a first detection signal that is generated from said first exhaust sensor, and a second feedback control is executed to correct the first feedback control value by judging a deterioration state of the catalyst material on the basis of a second detection signal that is generated from the second exhaust sensor, characterized by a control means for controlling in a manner such that when catalyst deterioration judging conditions are satisfied, the second feedback control value upon judgment of the deterioration is set in correspondence to the second feedback control value in the case where the catalyst deterioration judging conditions are not satisfied, the sum of a rich inversion delay time and a lean inversion delay time is set to a predetermined value, a ratio of the rich inversion delay time and a ratio of the lean inversion delay time are set to be equal, a correction amount of the first feedback control value is set to be larger than a correction amount in the case where the catalyst deterioration judging conditions are not satisfied, and an integration judging time of the second feedback control value in the case where the catalyst deterioration judging conditions are satisfied is set to be shorter than an integration judging time in the case where the catalyst deterioration judging conditions are not satisfied.
Also according to a construction of the present invention, the control means controls in a manner such that when the catalyst deterioration judging conditions are satisfied, the second feedback control value upon judgment of the deterioration is set in correspondence to the second feedback control value in the case where the catalyst deterioration judging conditions are not satisfied, the sum of the rich inversion delay time and the lean inversion delay time is set to a predetermined value, the ratio of the rich inversion delay time and the ratio of the lean inversion delay time are set to the same value, the correction amount of the first feedback control value is set to be larger than that in the case where the catalyst deterioration judging conditions are not satisfied, and the integration judging time of the second feedback control value in the case where the catalyst deterioration conditions are satisfied is set to be shorter than that in the case where the catalyst deterioration conditions are not satisfied. Due to this, the deterioration judging precisions of the catalyst material and the exhaust sensors are improved. A measurement variation amount of the deterioration judgment is reduced in the case where the catalyst deterioration judging conditions are satisfied is reduced. An amount of exhaust harmful components which are generated upon switching between the second feedback control values when the catalyst deterioration judging conditions are not satisfied and when the catalyst deterioration judging conditions are satisfied can be reduced. Moreover, the variation of the response delay time can be also decreased.
According to a third embodiment of the present invention, there is provided an apparatus for judging deterioration of a catalyst material of an internal combustion engine comprising: first and second exhaust sensors which are respectively provided on an exhaust passage of the internal combustion engine on the upstream side and downstream side of the catalyst; and control means for performing a first feedback control to set an air fuel ratio to a target value on the basis of a first detection signal which is generated from the first exhaust sensor and for performing a second feedback control to correct the first feedback control by a second detection signal which is generated from the second exhaust sensor, characterized in that the control means has a judging section such that in the case where predetermined deterioration judgment performing conditions are satisfied, the number of first detection signal periods and the number of second detection signal periods in a predetermined arithmetic operating time are measured from periods of time during which the first and second detection signals are inverted, thereby calculating a period ratio, a first detection signal surrounding area and a second detection signal surrounding area in the predetermined arithmetic operating time are measured from areas which are surrounded by loci of the periods of time during which the first and second detection signals are inverted, thereby calculating an area ratio, an operation state value in the predetermined arithmetic operating time is measured from an operating state of the internal combustion engine, thereby calculating a correction value, deterioration judgment arithmetic operation values in which the period ratio and the area ratio have been corrected by the correction value are obtained, and an arithmetic operation is performed so as to judge a deterioration state of the catalyst material by the deterioration judgment arithmetic operation values.
According to the construction of the third embodiment of the invention, in the case where the predetermined deterioration judgment performing conditions are satisfied, the deterioration judgment arithmetic operation values in which the period ratio and the area ratio of the first and second detection signals have been corrected by the correction value are obtained by the judging section provided for the control means, and the deterioration state of the catalyst is calculated by the deterioration judgment arithmetic operation values. As mentioned above, not only the period ratio of the first and second detection signals but also the area ratio are calculated and multiplied and the deterioration judgment arithmetic operation values corrected by the correction value are obtained and the judgment is performed. Thus, the deterioration state of the catalyst can be correctly measured and the judging precision of the deterioration state can be improved.